1. Field of the Invention
The present invention relates to a method of cooling a heat treatment bath, such as a salt bath in which hot workpieces are quenched in regular succession or at random intervals.
2. Description of the Prior Art
The idea of using a salt bath for the heat treatment of workpieces, which are to be quenched in regular succession or at varying intervals, using a bath temperature somewhere within the range of 400.degree. to 550.degree. C, is known from the prior art in this field. In order to achieve certain specific material characteristics of the workpieces treated, it is necessary to maintain the temperature of such a salt bath at a predetermined value within the aforementioned temperature range. In the case where such a salt bath is used to heat workpieces to be treated, the maintenance of a given temperature of the salt bath requires the addition of heat to the bath to keep it at the desired temperature level. If, on the other hand, the workpieces which are introduced into the salt bath are hot, having a temperature which is higher than the prescribed temperature of the salt bath, a corresponding removal of heat, by controlled cooling of the bath, will be necessary.
The first-mentioned situation, viz., the supply of heat to the treatment bath, can be accomplished with the same heating means that is normally used for the initial melting of the salt, using an induction heater, for example. The second requirement, involving removal of heat through cooling of the salt bath, is more difficult to satisfy. It necessitates a heat exchanger and a cooling medium circuit, using water, for example. Such a cooling installation may require large quantities of water, and known installations of this type have been the source of dangerous salt bath explosions, in the event that the heat exchanger, which is immersed in the hot salt bath, suffers a fracture through which large quantities of water can escape into the salt melt. In direct contact with the latter, the water evaporates almost instantaneously, expanding with explosive force.